organ. The cell bodies of the second neurons form a collection outside the CNS, called
(1) The first neuron extends from the CNS to the ganglion and is therefore
called the preganglionic neuron.
(2) Cell bodies of the second neuron make up the ganglion. The second
neuron's processes extend from the ganglion to the visceral organ. Thus, the second
neuron is called the post-ganglionic neuron.
c. Major Divisions of the Human ANS. The efferent pathways of the ANS fall
into two major divisions:
(1) The thoraco-lumbar outflow (sympathetic nervous system).
(2) The cranio-sacral outflow (parasympathetic nervous system).
d. Major Activities of the Human ANS.
(1) The ANS maintains visceral activities in a balanced or stable
state. This is called homeostasis.
(2) When subjected to stress, such as a threat, the body responds with the
"fight-or-flight reaction." That is, those activities of the body necessary for action in an
emergency are activated and those not necessary are deactivated. This is the primary
function of the sympathetic portion of the ANS.
11-17. THE THORACO-LUMBAR OUTFLOW (SYMPATHETIC NERVOUS SYSTEM)
a. Refer to paragraph 11-10b(2) which describes the H-shaped region of gray
matter in the cross section of the spinal cord. Imagine extending the cross link of the H
slightly to the left and right of the vertical arms; the extended ends would correspond to
the intermediolateral gray columns. Cell bodies of the first neurons of the sympathetic
NS make up those columns between the T-1 and L-2 levels of the spinal cord, a total of
14 levels. Here, we are speaking of preganglionic sympathetic neurons.
b. Cell bodies of the second neurons make up various sympathetic ganglia of
the body. These ganglia include the trunk or chain ganglia and the pre-aortic or
"central" ganglia. Here, we are speaking of post- ganglionic sympathetic neurons.
c. The sympathetic NS innervates:
(1) Peripheral visceral organs (example: sweat glands).
(2) Central visceral organs (examples: lungs and stomach).